From: "Ihar 'Philips' Filipau" <filia@softhome.net>
To: root@chaos.analogic.com
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Incremental update of TCP Checksum
Date: Wed, 17 Sep 2003 16:06:43 +0200 [thread overview]
Message-ID: <3F686A73.9080706@softhome.net> (raw)
In-Reply-To: <wKxN.5h0.7@gated-at.bofh.it>
Richard B. Johnson wrote:
>
> This is all wonderful. This assumes that the stuff being modified
> in the packet is on well-defined boundaries, seldom the case when
> you are re-writing packet data, but certainly the case if you
> are re-writing an IP address.
>
> Also, modern switches do not rewrite checksums using software.
^^^^^^^^
> Therefore, they do not use a re-write algorithm as stated by
> others. The checksum gets calculated "for free" during the
> hardware transfer to an output holding FIFO. It is done using
> an ASIC with the appropriate adder and "stumble-carry".
>
It depends on definition of software. It is so hard to draw parallel
especially when what looks like controller runs some flavour of Linux
from some embedded flash ;-)
Actually some switches do alter header _before_ they have received
payload. Just to be able to start rx without waiting for payload to
arrive completely. Sometimes low latencies (even on narrow bandwidth
links) are _that_ important...
--
Ihar 'Philips' Filipau / with best regards from Saarbruecken.
- - - - - - - - - - - - - - - - - - - -
* Please avoid sending me Word/PowerPoint/Excel attachments.
* See http://www.fsf.org/philosophy/no-word-attachments.html
- - - - - - - - - - - - - - - - - - - -
There should be some SCO's source code in Linux -
my servers sometimes are crashing. -- People
next parent reply other threads:[~2003-09-17 14:05 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <kysi.5h.17@gated-at.bofh.it>
[not found] ` <mZy6.3NX.7@gated-at.bofh.it>
[not found] ` <wtdD.3EP.13@gated-at.bofh.it>
[not found] ` <wtnf.3Zv.9@gated-at.bofh.it>
[not found] ` <wuMz.65Q.15@gated-at.bofh.it>
[not found] ` <wBkH.7Sv.3@gated-at.bofh.it>
[not found] ` <wKxN.5h0.7@gated-at.bofh.it>
2003-09-17 14:06 ` Ihar 'Philips' Filipau [this message]
2003-08-14 22:06 Netfiltering - NF_IP_LOCAL_OUT - how it works??? Vishwas Raman
2003-08-21 13:49 ` Harald Welte
2003-09-16 18:50 ` Incremental update of TCP Checksum Vishwas Raman
2003-09-16 19:00 ` Valdis.Kletnieks
2003-09-16 20:32 ` Vishwas Raman
2003-09-16 20:47 ` Leo Mauro
2003-09-17 3:28 ` Raf D'Halleweyn
2003-09-17 4:43 ` David S. Miller
2003-09-17 13:20 ` Richard B. Johnson
2003-09-17 20:34 ` Jamie Lokier
2003-09-16 19:47 ` Richard B. Johnson
2003-09-16 20:21 ` Vishwas Raman
2003-09-16 20:34 ` Richard B. Johnson
2003-09-16 20:35 ` Jesper Juhl
2003-09-17 1:37 ` Lincoln Dale
2003-09-17 1:39 ` Jesper Juhl
2003-09-16 22:41 ` Jamie Lokier
2003-09-16 23:32 ` Vishwas Raman
2003-09-16 20:33 ` Patrick McHardy
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